Cardiovascular Part 4 Flashcards
Arteries
- Near the heart, e.g. the aorta
- Large lumen (low resistance)
- More elastic tissue (elastic tubes)
- Pressure reservoirs
- During systole, arteries stretch.
- During diastole, the arteries recoil= maintaining blood flow through the body.
Compliance
How easily a structure stretches
Δvolume / Δ pressure
The higher the compliance of a structure, the more easily it can be
stretched.
Atherosclerosis
narrowing
Arteriosclerosis
stiffening
Hypertension
BP of about 140/90 mmHg
Pulse Pressure
Difference between systolic and diastolic pressures (120 – 80 = 40 mmHg ).
- Felt as a pulsation in the arteries of the wrist or neck with each heartbeat as artery expands & recoils
- The factors affecting pulse pressure include:
(1) Stroke volume
(2) Speed of ejection of the stroke volume
(3) Arterial compliance
Arterioles
- Smallest arteries
- Surrounded by smooth muscle
- Controlled by
– Neural
– Hormonal
– Local signals - Control minute-to-minute blood flow into capillary beds
– Constriction → blood flow is diverted away from tissue
– Dilation → blood flow to tissue increases.
F = ∆P / R
Systemic Controls
SNS activation affects blood vessel diameter
Arteriolar response depends on receptors encountered:
-Alpha adrenergic receptors (α1 & α2)
Binding of NE & E cause vasoconstriction
-Beta adrenergic receptor (β2)
Binding of E causes vasodilation
* No significant PNS effects
Vasomotor Tone
* Controlled by the vasomotor center in the medulla oblongata
* Regulated primarily by α-receptors (SNS)
* More APs= vasoconstriction
* Fewer APs= vasodilation via blood pushing open vessels
Local regulation
Endothelial cells secrete autocrine and paracrine agents
– Induce contraction or relaxation of adjacent smooth muscle
– Local regulation Plays a role in two key mechanisms of blood flow control:
1. Active hyperemia
2. Flow Autoregulation
Systemic & Local Controls
- Nitric oxide (NO) ANS neurons
- Nitric oxide causes vasodilation
- Major sites of action
Penis
Clitoris
GI tract (enteric nervous system) - Viagra (sildenafil) inhibits PDE-5
- cGMP accumulates to increase effects of nitric oxide
Capillaries
Smallest blood vessels
Site of gas and nutrient exchange
Diffusion of “good stuff” out of the blood into the tissues
Diffusion of “bad stuff” back into the blood
Anatomy of Capillary Network
Velocity is slowest in the capillary beds
Greater total cross-sectional area
1- Active hyperemia (Metabolic Control)
2- Flow Autoregulation (Myogenic Control)
Veins
Less smooth muscle, elastin and thinner walls than arteries
Highly distensible
Called capacitance vessels
Act as blood reservoirs
Blood pressure in veins is ~15 mm Hg
Not sufficient to move blood back to the heart
Venous Pressure
Varicose Veins
Valves prevent the backflow of venous blood
* Varicose veins
* Veins become dilated
* Due to incompetent (leaky) valves
* About 15% of adults
* mainly in the lower limbs
Varicose Veins
- Valves prevent the backflow of venous blood
- Varicose veins
- Veins become dilated
- Due to incompetent (leaky) valves
- About 15% of adults
- mainly in the lower limbs
Baroreceptors
- Stretch receptors @
- Aorta arch
- Carotid sinus
- Heart wall
Hypotension
Circulatory Shock
Hypovolemic
* Most common
* Large loss of blood volume
* Hemorrhage
* Severe vomiting
* Severe diarrhea
* Extensive burns
* Pulse is weak, heart rate increases to try to compensate
* Fluids lost must be replaced to maintain blood flow
Cardiogenic
* Pump failure
* The heart cannot sustain adequate
circulation
* This is usually the result of myocardial
damage following a severe MI or
multiple MIs
Vascular
* Extreme vasodilation
* Usually associated with septic shock or neurogenic shock
Hypertension
Chronically elevated blood pressure.
* A “silent” killer
* Prolonged hypertension is the major cause of heart failure,
renal failure, stroke, and vascular disease.
* Factors:
– Diet: high Na+, high cholesterol, etc.
– Obesity
– Age > 40
– Gender (males get it more than females until menopause)
– Genetics
– Stress
– Smoking
* No cure. Manage with diet, exercise, life-style changes, and medication (diuretics, beta blockers)
